Taper Junction Subsidence Occurs in Modular Tumor Endoprostheses: How Concerned Should We Be?
Bibliographic record
Abstract
BACKGROUND: Advancements in musculoskeletal oncologic treatment have allowed for longer survival of patients with malignant bone tumors and the associated longer use of tumor endoprostheses in those who have had such reconstructions. Several studies have reported on increased serum metal ions with the use of such implants. Modularity in these implants introduces the risk of taper junction corrosion and subsidence resulting in metal wear particle release that may cause an adverse local tissue reaction or systemic toxicity. Additionally, these implants contain a large surface area of cobalt and chromium. It is unclear whether the source of the increased serum ion levels was due to the taper junction corrosion or the implant itself. To our knowledge, no prior study has reported on taper junction subsidence. QUESTIONS/PURPOSES: In this study we sought (1) to determine survivorship free from radiographic taper junction subsidence in a femoral modular tumor endoprosthesis, and (2) to identify the implant characteristics in the endoprostheses associated with taper subsidence. METHODS: Between January 1996 and February 2020, the senior author performed 150 proximal or distal femur replacements following resections of soft tissue or bone tumors of the thigh and femur. Of those, 6% (9 of 150) of patients were lost to follow-up before 2 years, 25% (37 of 150) could not be analyzed due to absence of plain radiographs during follow-up, and 13% (20 of 150) died before 2 years follow-up, leaving 56% (84 of 150) for analysis in this retrospective study, with a median time for analysis of 14 years (range 2 to 31 years) after the index resection and endoprosthetic reconstruction for patients with distal femur replacements and 5 years (range 2 to 19 years) for patients with proximal femur replacement. Radiographs involving the entire implant were evaluated for the presence or absence of subsidence of the taper junction that was evident and clear to see if present. The association between the number of taper junctions, the length of resection, the number of collapsed junctions, and the time to collapse from the initial surgery were examined using regression analysis. RESULTS: Overall, 14% (12 of 84) patients with a distal femur replacement had radiographic collapse of at least one of the modular tapers. Survivorship free from taper subsidence was 91% (95% CI 86% to 96%) at 10 years and 84% (95% CI 78% to 90%) at 20 years. All patients were in the distal femur replacement group. The median follow-up of patients with subsidence was 15 years (range 5 to 26). Fifty-eight percent (7 of 12) of patients had two junctions involved, 25% (3 of 12) had three junctions, and 17% (2 of 12) had one junction involved. All but one patient had subsidence in a single junction. The median time to subsidence was 15 years (range 4.5 to 24.0 years). The subsidence was progressive in all patients who demonstrated it. The taper junction subsidence was complete in 75% (9 of 12) of patients and partial in 25% (3 of 12). Univariate and multivariable regression analyses did not show that the risk factors we studied were associated with subsidence. Two patients with junction subsidence were revised, one for taper fracture and one during busing exchange for distal junction subsidence. CONCLUSION: Taper damage with late and progressive subsidence of the intervening junction is not uncommon after distal femur replacement. The impact of such a complication is still unknown. Further studies should examine the long-term outcomes and correlate them with metal ion levels. LEVEL OF EVIDENCE: Level III, therapeutic study.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.005 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".